Biomechanical Comparison of Fixation of Metacarpal Shaft Fractures With Intramedullary Threaded Nail and Dorsal Plate.

The purpose of this study was to investigate the mechanical properties of metacarpal long oblique and transverse shaft fractures stabilized by threaded intramedullary nails and dorsal plates and screws. Transverse and oblique midshaft osteotomies were created in 28 paired left and right metacarpal bones from four fresh frozen cadavers. Each matched pair was fixed with one 4.5-mm threaded intramedullary nail and one 2.0-mm dorsal stainless-steel plate and a screw construct. The bones were secured at the proximal end, by a 3-D-printed customized jig, to a tensile testing machine and were loaded through a Kevlar wire tensioned over the metacarpal head, simulating muscle/tendon loading during grip. Loading to failure was performed, and the applied force and failure mode were recorded. Oblique fractures fixed with nails failed at a greater force than those fixed with dorsal plates (183 ± 50 N vs 130 ± 40 N). Transverse fractures showed comparable strength between the nail (215 ± 33 N) and the plate (183 ± 64 N). Plate failure modes included three diverse types of bone fracture and yielding deformation of the plate. Intramedullary nail failure modes included yielding of the nail, bone fracture without nail yielding, and relative rotation between the two sections of the bone. Fixation of oblique and transverse metacarpal shaft fractures using a 4.5-mm threaded intramedullary nail in a simulated grip test model showed similar or greater strength than a 2.0-mm dorsal plate and screw construct. Threaded intramedullary nail fixation of metacarpal shaft fractures may be an appropriate alternative to plate fixation in these fracture patterns.

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